.TH std::mutex 3 "2024.06.10" "http://cppreference.com" "C++ Standard Libary"
.SH NAME
std::mutex \- std::mutex

.SH Synopsis
   Defined in header <mutex>
   class mutex;               \fI(since C++11)\fP

   The mutex class is a synchronization primitive that can be used to protect shared
   data from being simultaneously accessed by multiple threads.

   mutex offers exclusive, non-recursive ownership semantics:

     * A calling thread owns a mutex from the time that it successfully calls either
       lock or try_lock until it calls unlock.
     * When a thread owns a mutex, all other threads will block (for calls to lock) or
       receive a false return value (for try_lock) if they attempt to claim ownership
       of the mutex.
     * A calling thread must not own the mutex prior to calling lock or try_lock.

   The behavior of a program is undefined if a mutex is destroyed while still owned by
   any threads, or a thread terminates while owning a mutex. The mutex class satisfies
   all requirements of Mutex and StandardLayoutType.

   std::mutex is neither copyable nor movable.

.SH Member functions

   constructor   constructs the mutex
                 \fI(public member function)\fP
   destructor    destroys the mutex
                 \fI(public member function)\fP
   operator=     not copy-assignable
   [deleted]     \fI(public member function)\fP
.SH Locking
   lock          locks the mutex, blocks if the mutex is not available
                 \fI(public member function)\fP
   try_lock      tries to lock the mutex, returns if the mutex is not available
                 \fI(public member function)\fP
   unlock        unlocks the mutex
                 \fI(public member function)\fP
.SH Native handle
   native_handle returns the underlying implementation-defined native handle object
                 \fI(public member function)\fP

.SH Notes

   std::mutex is usually not accessed directly: std::unique_lock, std::lock_guard,
   or std::scoped_lock
   \fI(since C++17)\fP manage locking in a more exception-safe manner.

.SH Example

   This example shows how a mutex can be used to protect an std::map shared between two
   threads.


// Run this code

 #include <chrono>
 #include <iostream>
 #include <map>
 #include <mutex>
 #include <string>
 #include <thread>

 std::map<std::string, std::string> g_pages;
 std::mutex g_pages_mutex;

 void save_page(const std::string& url)
 {
     // simulate a long page fetch
     std::this_thread::sleep_for(std::chrono::seconds(2));
     std::string result = "fake content";

     std::lock_guard<std::mutex> guard(g_pages_mutex);
     g_pages[url] = result;
 }

 int main()
 {
     std::thread t1(save_page, "http://foo");
     std::thread t2(save_page, "http://bar");
     t1.join();
     t2.join();

     // safe to access g_pages without lock now, as the threads are joined
     for (const auto& [url, page] : g_pages)
         std::cout << url << " => " << page << '\\n';
 }

.SH Output:

 http://bar => fake content
 http://foo => fake content

.SH See also

   recursive_mutex    provides mutual exclusion facility which can be locked
   \fI(C++11)\fP            recursively by the same thread
                      \fI(class)\fP
   lock_guard         implements a strictly scope-based mutex ownership wrapper
   \fI(C++11)\fP            \fI(class template)\fP
   unique_lock        implements movable mutex ownership wrapper
   \fI(C++11)\fP            \fI(class template)\fP
   scoped_lock        deadlock-avoiding RAII wrapper for multiple mutexes
   \fI(C++17)\fP            \fI(class template)\fP
   condition_variable provides a condition variable associated with a std::unique_lock
   \fI(C++11)\fP            \fI(class)\fP
